A mini-set that was featured in Harbinger Magazine. Sold together with "Hilltop Encounter" as the Deadly Encounters Combo.
From the publisher's website:
SACRIFICIAL PORTAL INCLUDES:
* 2 black portal spires (can be used individually to create more elaborate ritual areas)
* 1 towering central portal opening
* 1 diorama base tile with blood stained central sacrifice area
* 2 7"X7" base tiles with blood stained central sacrifice area (both gridded & non-grid versions)